This invention relates to in-mold coating compositions in general and, more particularly, to low-temperature curing in-mold coating compositions.
Fiber reinforced plastic (FRP) parts are typically made by a compression molding process. In a conventional compression molding process, a curable resin charge is placed between a pair of heated die members defining a mold cavity. The die members are then moved toward each other to a closed position, thereby compressing the resin charge and causing the resin charge to flow and fill the mold cavity. After the resin cures, the molds are opened and the finished part is removed.
The resin charge used to make an FRP part generally includes a thermosetting resin containing reinforcing fibers and various fillers. The charge is typically a sheet molding compound (SMC), which typically contains a thermosetting resin, about 30% by weight of glass fibers, shrink-reduction additives, and a large amount of filler. The charge, however, may also be a high strength molding compound (HMC), which typically contains a thermosetting resin, and about 50 to 60% by weight of glass fibers with very little, if any, filler or shrink-reduction additives. Because of the high glass content and lack of filler and shrink-reduction additives, an HMC part tends to shrink considerably more than an SMC part upon cooling.
The surface of an FRP part prepared by a compression molding process is often blemished with cavities, pinholes, cracks, and/or sinkers, which would make the FRP part unacceptable for many commercial applications. In recent years, however, it has become common to use what is known as an xe2x80x9cin-mold coatingxe2x80x9d to provide an FRP part with a commercially acceptable smooth finish. Examples of xe2x80x9cin-mold coatingxe2x80x9d methods are disclosed in U.S. Pat. No. 4,076,788 to Ditto, and U.S. Pat. No. 4,668,460 to Ongena, which are hereby incorporated by reference herein. Briefly, in an xe2x80x9cin-mold coatingxe2x80x9d method, the cured FRP part remains in the mold and is coated with a composition that spreads and penetrates the surface to fill the cavities, etc. formed therein.
The prior art compositions used in xe2x80x9cin-mold coatingxe2x80x9d methods are typically cured at a temperature of about 300xc2x0 F., which is acceptable for many SMC parts. For other FRP parts and other compression-molded products, however, this temperature is too great. For example, it is desirable to xe2x80x9cin-mold coatxe2x80x9d an HMC part at a much lower temperature to permit the HMC part to shrink. Prior art compositions have been developed that cure at temperatures lower than 300xc2x0 F., but these compositions have extremely short pot-lives, which make them difficult to work with.
Based upon the foregoing, there is a need in the art for an in-mold coating composition that can be cured at a temperature lower than 300xc2x0 F. and still has a workable potlife. The present invention is directed to such an in-mold coating composition and a method of using the same.
It therefore would be desirable, and is an advantage of the present invention, to provide an in-mold coating composition curable at a temperature below 300xc2x0 F. The in-mold coating composition includes from about 140 to about 325 parts by weight of a polymerizable resin, from about 1 to about 4 parts by weight of a promoted peroxide that includes a tertiary organic perester, from about 1 to about 6 parts by weight of a polymer-bound catalyst that includes a transition metal physically bound to a polymeric composition, and from about 0.2 to about 2 parts by weight of an amine synergist that includes at least one aromatic tertiary amine.
Also provided in accordance with the present invention is a thermosetting in-mold coating composition that includes 100 parts by weight of a polyacrylate monomer, from about 10 to about 60 parts by weight of a urethane acrylate oligomer, from about 30 to about 165 parts by weight of at least one ethylenically unsaturated monomer, from about 1 to about 4 parts by weight of a promoted peroxide that includes a tertiary organic perester and an enolizable ketone, from about 1 to about 6 parts by weight of a polymer-bound catalyst that includes a transition metal physically bound to a polymeric composition, and from about 0.2 to about 2 parts by weight of an amine synergist that includes a mixture of an N-alkyl-N-hydroxyalkyl-p-toluidine and at least one other aromatic tertiary amine different from the N-alkyl-N-hydroxyalkyl-p-toluidine.
Further provided in accordance with the present invention is an in-mold coating method wherein a charge is provided comprising a thermosetting resin and reinforcing fibers. The charge is molded into a desired shape at an elevated pressure and then at least partially cured to form a substrate. The substrate is coated with a thermosetting in-mold coating composition, which is cured at a temperature less than 300xc2x0 F. The in-mold coating composition includes from about 140 to about 325 parts by weight of a polymerizable resin, from about 1 to about 4 parts by weight of a promoted peroxide that includes a tertiary organic perester, from about 1 to about 6 parts by weight of a polymer-bound catalyst that includes a transition metal physically bound to a polymeric composition, and from about 0.2 to about 2 parts by weight of an amine synergist that includes at least one aromatic tertiary amine.